One of the more widely practiced decaffeination methods is the process disclosed by Berry et al. in U.S. Pat. No. 2,309,092, the so-called water decaffeination technique. Green coffee beans are first moistened and then extracted with a caffeine-deficient green coffee extract in a multi-stage countercurrent extraction battery. While progressing through the extraction battery, the green coffee extract becomes increasingly rich in caffeine and contacts decreasingly decaffeinated beans. Periodically, the stage containing the most highly decaffeinated coffee is isolated from the battery and a stage containing fresh green beans is placed on stream. Caffeine-laden coffee extract is withdrawn from the last stage of the extraction battery, processed so as to remove the caffeine therefrom and returned to the system as caffeine-deficient green coffee extract. The caffeine is removed from the caffeine-laden extract by contact with an organic solvent, most preferably a halogenated hydrocarbon solvent, such as trichloroethylene or methylene chloride. The water decaffeination technique, although it currently has wide application in the industry, is directed only to the decaffeination of green coffee beans and is not suited to the more efficient decaffeination of roasted coffee extracts.
While techniques are known for decaffeinating roasted coffee extracts, the methods are not without certain drawbacks. For example, Belgian Patent Disclosure No. 865,488 of Bolt et al. describes a process wherein the coffee extract is first decaffeinated with a solvent; the solvent is then contacted with water to transfer the caffeine and unavoidably, some non-caffeine solubles; the decaffeinated solvent is returned to the coffee extract and stripped therefrom; and the caffeine is crystallized from the water phase, which is then discarded. The water phase inevitably contains some non-caffeine solubles which would contribute important body notes to the soluble coffee but are instead discarded. A similar though supposedly improved method is disclosed in U.S. Pat. No. 4,409,253 to Morrison et al. The improvement consists of recyclying the water phase from which the caffeine has been crystallized back to the original caffeine-containing extract. The water phase apparently cannot be combined with the decaffeinated extract because the crystallization leaves substantial caffeine in the water. Hence, the inefficient recycle of the water phase, with the accompanying increase in the amount of caffeine to be removed, is needed.
A complexation approach to the decaffeination of roasted coffee extracts is also known. Caffeic acid is suspended in the roasted coffee extract or the caffeic acid may be dissolved in water and the solution added to the extract. An insoluble, colloidal caffeic acid/caffeine complex forms almost instantaneously, but it is virtually impossible to separate the colloidal complex from the coffee extract. Larger crystals of the complex which are more easily separable will grow on standing but the growth is quite slow, taking upwards of two weeks. Manipulation of the extract pH or temperature promotes more rapid crystal growth but the process is not as fast as is commercially desirable. The chief advantage of the complexation approach is that essentially only the caffeine is removed and virtually all of the non-caffeine coffee solubles initially present remain in the decaffeinated roasted coffee extract.
It is an object of the present invention to provide a roasted coffee extract decaffeination method which produces a soluble coffee of improved flavor.
A further object of the invention is to provide a coffee extract decaffeination method using a complexation approach which is faster than complexing caffeic acid and caffeine directly in the roasted coffee extract.